title: Tuning electron transfer rates through molecular bridges in quantum dot sensitized oxides.
abstract: Photoinduced electron transfer processes from semiconductor quantum dots (QDs) molecularly bridged to a mesoporous oxide phase are quantitatively surveyed using optical pump-terahertz probe spectroscopy. We control electron transfer rates in donor-bridge-acceptor systems by tuning the electronic coupling strength through the use of n-methylene (SH-[CH2]n-COOH) and n-phenylene (SH-[C6H4](n)-COOH) molecular bridges. Our results show that electron transfer occurs as a nonresonant quantum tunneling process with characteristic decay rates of β(n) = 0.94 ± 0.08 and β(n) = 1.25 per methylene and phenylene group, respectively, in quantitative agreement with reported conductance measurements through single molecules and self-assembled monolayers. For a given QD donor-oxide acceptor separation distance, the aromatic n-phenylene based bridges allow faster electron transfer processes when compared with n-methylene based ones. Implications of these results for QD sensitized solar cell design are discussed.
authors.affiliation: Max Planck Institute for Polymer Research , Ackermannweg 10, 55128 Mainz, Germany.
authors.forename: Hai
authors.initials: H
authors.lastname: Wang
authors.forename: Erik R
authors.initials: ER
authors.lastname: McNellis
authors.forename: Sachin
authors.initials: S
authors.lastname: Kinge
authors.forename: Mischa
authors.initials: M
authors.lastname: Bonn
authors.forename: Enrique
authors.initials: E
authors.lastname: Cánovas